Study the clinical application and detection of cardiac troponin
Since the 1990s, cardiac troponin (cTn) has been used in clinical diagnosis of myocardial injury. Due to its high specificity and good sensitivity, it is quickly accepted by clinicians and inspectors.
First, the clinical application of cTn
The initial cTn application report focused on clinical applications of myocardial enzyme markers such as CK-MB, such as diagnosis, risk estimation, and prognostic value in myocardial infarction (MI) and angina, and clinical thrombolytic therapy after MI. determination. Other applications of cTn in the diagnosis and treatment of heart disease have subsequently been reported, such as in the diagnosis of various myocardial injuries (myocarditis, myocardial trauma, cardiac surgery, perioperative cardiac complications, severe sepsis, and sepsis) Left heart failure, congestive heart failure and other diseases) and the estimation of myocardial ischemic injury area, the application of estimated left ventricular function, and the clinical efficacy of certain therapeutic drugs, and so on.
Second, some important documents about the clinical application of cTn
In recent years, the Chinese Medical Association Inspection Society, the International Union of Clinical Chemistry (IFCC), the American Society of Clinical Biochemistry (NACB), the European Society of Cardiology (ESC), the American College of Cardiology (ACC), and the American Heart Association (AHA) have been at home and abroad. The relevant academic community has published many important documents on cTn clinical application recommendations or guidelines. These documents agree that cTn is a good marker for the diagnosis of myocardial injury; elevated cTn indicates myocardial damage, but can be asymptomatic MI or ischemic injury without obvious symptoms; Blood damage should be considered for other causes of myocardial damage; elevated cardiac troponin indicates that myocardial damage is irreversible. With the application of cTn, previous detection items (such as AST, LD, HBDH, etc.) that measure enzyme activity should not be used in the diagnosis of MI. These documents also present many requirements or recommendations on how to make cTn more scientifically applicable.
Third, cTn clinical detection research
Many experts and scholars have carried out research on cTn clinical tests, and respectively applied methodological evaluations of clinical applications of certain cTn detection methods. Some studies are large in scale. In order to make the detection of cTn more reliable, more collaborative research by several hospital inspection departments is needed. These studies not only provide valuable clinical information, but can also be used to evaluate method reliability before and during analysis.
A large number of clinical studies have confirmed that cTnT or cTnI have the same clinical value in detecting myocardial injury. However, there are inconsistencies between different cTn (mainly cTnI) detection methods, and the results of various detection methods are different, which brings confusion to clinicians and inspectors. This has caused great concern to clinicians, inspectors and manufacturers. Standardization of detection (mainly cTnI detection standardization) will help solve some of these problems. Due to the unremitting efforts of academic organizations, experts, scholars and manufacturers, recent breakthroughs have been made in the standardization of cTnI reference materials, but there are still many problems in the standardization of cTn (mainly cTnI). solve. It has now been possible to make certain measured values ​​of the cTnI method consistent, but this is not a true standardization. Test standardization and traceability require a complete test reference system (including primary reference materials made from purified cTn complexes; secondary reference materials from serum sources; reference methods for the assignment of secondary reference materials and evaluation of conventional test methods) ), work in this area is still facing many difficulties. One of the important aspects of standardization is to establish a cTn reference range and detection limit for different detection methods. Before the standardization is achieved, the reference range and clinical decision limit can only be different depending on the detection method (method).
How to determine the upper limit of the reference range of cTn has undergone a process of change. In 1999, the relevant documents of IFCC and NACB respectively considered that cTn should choose two critical values, exceeding the low critical value (the 97.5th percentile value of the measured value of healthy population) indicates the presence of myocardial damage, which is greater than the high critical value (in accordance with WHO). The test value for the AMI diagnostic criteria should be diagnosed by Tiger MI. IFCC and NACB recommend a low threshold for the 97.5th percentile of healthy populations, which is consistent with other clinical testing methods. The false positive rate of detection at this time was 2.5%. The 2000 ESC/ACC document redefines MI, suggesting that the upper limit of the reference range of cTn should take the 99th percentile of the measured value of the healthy population as a single critical point, which is the low threshold recommended by IFCC and NACB. Between the high threshold and the high value. The rationale for raising the low threshold from the 97.5th percentile to the 99th locus is to reduce the false positive rate of diagnosis of myocardial damage. Exceeding this threshold is accompanied by one of the following conditions, such as clinical chest pain ischemic symptoms, or pathological Q wave in the electrocardiogram, or ischemic changes (ST-segment elevation or depression), or coronary catheterization For abnormalities, etc., the diagnosis of MI can be considered. The 2000 and 2002 ACC/AHA documents were based on the ESC/ACC redefinition of MI, suggesting that patients with unstable angina who have elevated cTn but whose ST segment is not elevated in the electrocardiogram should be diagnosed as ST-segment elevation-free MI (NSTEMI). Both ESC/ACC and ACC/AHA documents have increased cTn as the primary condition for diagnosing myocardial injury, making it important to determine the 99th percentile of the cTn reference range for healthy populations. In accordance with the MI redefinition document, each manufacturer shall provide an upper limit (99th percentile value) of the cTn reference range for each method (measurement condition) determined based on the results of a joint study of multiple laboratories. This type of research is currently rare. These important documents at home and abroad also emphasize that the inspection department should analyze the cTn test results under their respective test conditions and establish appropriate threshold values ​​based on the ROC curve. Studies on the upper limit of the reference range of cTn and the establishment of a critical value based on the ROC curve are rarely reported in the country.
The requirement for the precision of cTn analysis is that the detection CV ≤ 10% at the 99th percentile of the upper limit of the reference range. Failure to meet this requirement would mislead the clinical risk. On the one hand, manufacturers should be required to actively work to improve the method to achieve this goal; on the other hand, the inspection department should also seriously consider this factor when evaluating and selecting cTn detection methods, especially when determining the critical value. Since most of the existing detection methods are difficult to detect cTn in healthy people, a minimum detection value capable of detecting CV ≤ 10% should be selected as a critical value for clinical application.
Non-specificity of the analysis can also lead to false positive results of the assay. It has been reported that heterophilic antibodies (rheumatoid-like factors or human anti-mouse antibodies) can cause false positive reactions (cTn pseudo-increased) in certain cTnI assays.
In addition, the current immunological technique (instrument) for detecting cTn has a wide detectable range, and it is generally rare to measure the sample after dilution. In case of dilution, it should be recognized that there may be a difference between the diluted measurement result and the original standard curve.
The use of plasma or whole blood samples to detect cTn saves the time required for blood agglutination, which shortens the preparation time before analysis and helps to shorten TAT. However, the results of plasma or whole blood samples are different from those of serum samples. Anticoagulants should be used with caution. When heparin is used for anticoagulation, cTn may affect the detected immune response due to binding to heparin; EDTA may cleave cTn complex, which may affect the accuracy of the test results. The effects of different anticoagulants on different types of specimens and the effects on specimens at different MI (early MI and late MI) specimens should also be considered. Manufacturers should strive to make the cTn test method applicable to both plasma (whole blood) and serum samples, or to make the cTn measurements of plasma (whole blood) samples consistent (or comparable) with serum samples.
The use of various myocardial injury markers (sample collection time) should take into account the respective diagnostic "window period". For various reasons, it is actually difficult to accurately understand the exact onset time of each chest pain patient. Therefore, it is generally considered to consider the specimen collection time according to the patient's visit time. Relevant academic groups and experts at home and abroad have obtained consistent opinions on the collection time of specimens of myocardial injury markers.
The detection turnaround time (TAT) of myocardial injury markers is very important for the timely diagnosis and treatment of patients with myocardial injury. Most of the important documents since 1999 require the detection of myocardial injury markers from the collection of specimens to the doctor to get a test report TAT ≤ 1 hour. The 2002 ACC/AHA document further requires that the myocardial injury marker TAT should preferably be ≤ 0.5 hours. The inspection department should be aware of the fact that it is inevitable to use appropriate POCT devices to detect myocardial injury markers when TAT is not met. The cost of detecting myocardial injury markers by POCT is relatively high. At present, there are few qualitative or semi-quantitative methods. It should be noted that the method of quantitative detection should be selected. Quantitative detection of myocardial injury markers using POCT can reduce specimen transport and processing time and help reduce reporting time. The inspection department should pay attention to strengthen the management of the use of POCT, strengthen the quality control, and train the operators to use the POCT device correctly to ensure the quality of the inspection.
There are many theoretical and practical problems and knowledge in the clinical application of cTn. Inspectors should read the literature carefully and select appropriate detection methods according to the specific situation. Although the cTn test has gradually become popular in China, there are still many problems in how to correctly understand and use it. There are few studies and evaluations on detection methods and clinical applications, and there are few studies and evaluations of large-scale multi-units in China. This is not conducive to the scientific and rational application of cTn clinical. Relevant academic organizations, inspection workers, and manufacturers should work together to advance this work.
Clinical application of cardiac troponin and detection of cardiac troponin
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